there is a prepaid meter in my house for gas can it be changed to a normal meter
Yes, but Bulb do charge £120 for switching from a pre-pay meter to a credit meter and require you to have been with them at least a month ( see https://help.bulb.co.uk/hc/en-us/articles/360016323991-Can-I-exchange-my-prepayment-meter- ).
However, Bulb will shortly (they’ve just started on small trial rollout, but a big rollout will happen next year) start deploying multi-provider compatible SMETS2 smart meters free of charge. These can be switched between tariffs remotely and so there should be no/very little fee for this (Bulb haven’t commented either way). So if you can stand being on pre-pay for between 1-12 months and want to save £120, it can be worth waiting.